Howard Hughes Medical Institute, Janelia Farm Research Campus, Ashburn, Virginia, United States of America.
PLoS Biol. 2010 Aug 24;8(8):e1000461. doi: 10.1371/journal.pbio.1000461.
Drosophila brains contain numerous neurons that form complex circuits. These neurons are derived in stereotyped patterns from a fixed number of progenitors, called neuroblasts, and identifying individual neurons made by a neuroblast facilitates the reconstruction of neural circuits. An improved MARCM (mosaic analysis with a repressible cell marker) technique, called twin-spot MARCM, allows one to label the sister clones derived from a common progenitor simultaneously in different colors. It enables identification of every single neuron in an extended neuronal lineage based on the order of neuron birth. Here we report the first example, to our knowledge, of complete lineage analysis among neurons derived from a common neuroblast that relay olfactory information from the antennal lobe (AL) to higher brain centers. By identifying the sequentially derived neurons, we found that the neuroblast serially makes 40 types of AL projection neurons (PNs). During embryogenesis, one PN with multi-glomerular innervation and 18 uniglomerular PNs targeting 17 glomeruli of the adult AL are born. Many more PNs of 22 additional types, including four types of polyglomerular PNs, derive after the neuroblast resumes dividing in early larvae. Although different offspring are generated in a rather arbitrary sequence, the birth order strictly dictates the fate of each post-mitotic neuron, including the fate of programmed cell death. Notably, the embryonic progenitor has an altered temporal identity following each self-renewing asymmetric cell division. After larval hatching, the same progenitor produces multiple neurons for each cell type, but the number of neurons for each type is tightly regulated. These observations substantiate the origin-dependent specification of neuron types. Sequencing neuronal lineages will not only unravel how a complex brain develops but also permit systematic identification of neuron types for detailed structure and function analysis of the brain.
果蝇大脑包含许多形成复杂回路的神经元。这些神经元是由固定数量的祖细胞（称为神经母细胞）以刻板的模式衍生而来的，鉴定由神经母细胞产生的单个神经元有助于重建神经回路。一种改良的 MARCM（可抑制细胞标记的马赛克分析）技术，称为双点 MARCM，允许同时以不同颜色标记来自共同祖细胞的姐妹克隆。它能够根据神经元出生的顺序鉴定出一个扩展神经元谱系中的每一个神经元。在这里，我们报告了第一个已知的来自共同神经母细胞的神经元的完整谱系分析的例子，这些神经元将嗅觉信息从触角叶（AL）中继到更高的大脑中枢。通过鉴定顺序衍生的神经元，我们发现神经母细胞连续产生 40 种 AL 投射神经元（PN）。在胚胎发生过程中，一个具有多肾小球传入的 PN 和 18 个针对成年 AL 的 17 个肾小球的单肾小球 PN 出生。在神经母细胞在早期幼虫中重新开始分裂后，会产生更多的 22 种额外类型的 PN，包括四种多肾小球 PN。虽然不同的后代以相当任意的顺序产生，但出生顺序严格决定了每个有丝分裂后神经元的命运，包括程序化细胞死亡的命运。值得注意的是，每个有丝分裂后神经元的命运是由其产生的神经母细胞的分裂次数决定的。胚胎期的祖细胞在每次自我更新的不对称细胞分裂后都具有改变的时间身份。幼虫孵化后，同一个祖细胞会为每种细胞类型产生多个神经元，但每种类型的神经元数量受到严格调控。这些观察结果证实了神经元类型的起源依赖性特化。对神经元谱系进行测序不仅可以揭示复杂大脑的发育方式，还可以允许系统地鉴定神经元类型，以对大脑进行详细的结构和功能分析。
